JP2012113055A5 - Imaging apparatus and photometric value calculation method - Google Patents

Description

In order to achieve the above object, an imaging apparatus according to the present invention includes a photometric unit that performs photometry of a subject and outputs a photometric value, and an acquisition unit that acquires a plurality of photometric values from the photometric unit without changing photometric conditions. Calculating means for calculating a photometric value used for exposure calculation based on the plurality of photometric values acquired by the acquiring means and output change characteristics of the photometric means .

The viewfinder mode selection switch SW138 switches between an optical viewfinder mode in which a subject can be confirmed by the eyepiece lens 106 and a live view display mode in which image signals from the image sensor 112 are sequentially displayed on the image display circuit 118. The communication interface circuit 126 performs an interface for communication with an external device under the control of the system controller 120.

The solid line in the figure is calculated based on the photometric output, and as the luminance becomes darker (the EV value becomes smaller), both the measurement error and the differential photometric value increase, and both are correlated. It shows that there is. Moreover, the broken line in the figure is obtained by fitting a graph indicated by a solid line with a cubic prediction function. As shown in FIG. 4, EV values are well matched from about 2 to -4, and it can be seen that photometry by prediction is possible. In addition, it is understood that the prediction accuracy is gradually lost at the luminance whose EV value is lower than −4. In an extremely low brightness such as an EV value of −6, in the initial state of waiting for stabilization after performing the reset operation and injecting carriers into the base of the phototransistor Q1, injected carriers are used as the emitter current component of the phototransistor Q1. Is overwhelmingly dominant. Therefore, it becomes difficult to obtain sufficient prediction accuracy. In order to improve the accuracy, the reading may be further performed and prediction may be performed by changing the order or coefficient of the prediction function. The number of readouts for prediction may be set to a well-balanced number in consideration of the release time lag allowed by the camera, shooting modes such as continuous shooting and single shooting, or the continuous shooting speed of the mounted camera. . Alternatively, depending on the camera, it is possible to cope with such as changing the stabilization waiting time for performing the predictive reading.

If ΔAE ≦ 0, the process proceeds to S715. If the value of ΔAE is −γ <ΔAE ≦ 0 in S715, the process proceeds to S716. When ΔAE is near 0, as a result, incident light is large to some extent, and the photometric circuit 107 is sufficiently stabilized during the prediction operation. Accordingly, the value of γ is set to a value of about 1/8 to 1/3, for example, based on the variation in photometric output and the allowable value of camera exposure. In S716, an average value of AE2 and AE3 is calculated, and based on this value, an exposure calculation is performed in S714, and this subroutine is terminated. In the case of ΔAE ≦ −γ, there is a change in the shooting scene, and it is considered that the subject brightness has changed brightly, so the process returns to S701 and re-photometry is performed.

Claims (12)

  A photometric means for measuring a subject and outputting a photometric value;
  Acquisition means for acquiring a plurality of photometric values from the photometric means without changing the photometric conditions;
  Calculation means for calculating a photometric value used for exposure calculation based on the plurality of photometric values acquired by the acquisition means and output change characteristics of the photometric means;
  An imaging device comprising:   The obtaining unit obtains a plurality of photometric values from the photometric unit without changing a photometric condition until a predetermined time elapses after the reset operation for the photometric unit, and the calculation unit includes the plurality of photometric values. 2. The imaging apparatus according to claim 1, wherein a photometric value used for the exposure calculation is calculated based on a photometric value and an output change characteristic of the photometric means.   The acquisition unit acquires a plurality of photometry values from the photometry unit without changing a photometry condition during a period when the photometry values output from the photometry unit are not stable, and the calculation unit calculates the plurality of photometry values. The imaging device according to claim 1, wherein a photometric value used for the exposure calculation is calculated based on an output change characteristic of the photometric means.   The obtaining unit obtains a plurality of photometric values from the photometric unit without changing the photometric condition in a period when the photometric value output from the photometric unit is not a photometric value corresponding to the luminance of the subject, and the computing unit 2. The imaging apparatus according to claim 1, wherein a photometric value used for the exposure calculation is calculated based on the plurality of photometric values and an output change characteristic of the photometric means.   The computing means is configured to change the first photometric value, the second photometric value, and an output change of the photometric means according to a difference between the first photometric value and the second photometric value among the plurality of photometric values. 5. The imaging apparatus according to claim 1, wherein whether or not to calculate a photometric value used for the exposure calculation is changed based on characteristics.   The second photometric value is a photometric value acquired after the first photometric value, and the calculating means is configured to calculate the first photometric value when the second photometric value is greater than or equal to the first photometric value. 6. The imaging apparatus according to claim 5, wherein the photometric value used for the exposure calculation is not calculated based on the photometric value, the second photometric value, and the output change characteristic of the photometric means.   The acquisition means acquires the third photometric value after acquiring the second photometric value when the first photometric value is greater than the second photometric value by a predetermined value or more,
  When the acquisition unit acquires the third photometric value, the calculation unit is used for the exposure calculation based on the third photometric value, the second photometric value, and the output change characteristic of the photometry unit. The imaging device according to claim 6, wherein a photometric value is calculated.   When the calculation means does not calculate the luminance of the subject based on the first photometry value, the second photometry value, and the output change characteristic of the photometry means, the first photometry value and the second photometry value The imaging device according to claim 6, wherein an average value is calculated as a photometric value used for the exposure calculation.   The computing means predicts a photometric value corresponding to the luminance of the subject based on the plurality of photometric values acquired by the acquiring means and an output change characteristic of the photometric means, and based on the predicted photometric value 9. The imaging apparatus according to claim 1, wherein a photometric value used for exposure calculation is calculated.   The calculation means calculates a photometric value used for the exposure calculation based on the plurality of photometric values acquired by the acquisition means and the output change characteristic of the photometric means before performing the first shooting of continuous shooting. The imaging apparatus according to claim 1, wherein no calculation is performed.   11. The output change characteristic of the photometry means is a characteristic that represents a relationship between a luminance of a subject and a photometric value, which changes according to an elapsed time since the start of photometry. The imaging device according to item.   A photometric value calculation method for calculating a photometric value using a photometric means for measuring a subject and outputting a photometric value,
  An acquisition step for acquiring a plurality of photometric values from the photometric means without changing the photometric conditions;
  A calculating step for calculating a photometric value used for exposure calculation based on the plurality of photometric values acquired in the acquiring step and an output change characteristic of the photometric unit;
  A photometric value calculation method comprising:

Images